1. Field of the Invention
The present invention relates to an optical module, and more particularly to an optical receiver of a bidirectional optical communication module, which is fabricated through an assembling process concurrent and integral with an assembling process applied to a wafer, and a method for fabricating the optical receiver.
2. Description of the Related Art
In general, each module is separately assembled when fabricating a communication optical module. If such a communication optical module is fabricated concurrently and integrally with an assembling process applied to a wafer, i.e., in which a plurality of modules are assembled at once, costs for the assembling process may be reduced, so the optical module can be fabricated at a low price.
FIGS. 1A and 1B are views showing a conventional structure of bidirectional optical communication module disclosed in U.S. Pat. No. 6,332,719. FIG. 1B is a sectional view taken along line A–A′ in FIG. 1A. Referring to FIGS. 1A and 1B, an optical fiber 130 is installed in a V-groove formed at an SiOB (Silicon Optical Bench) 120, and WDM filters 124, 125 are inserted into holes formed in the optical fiber. In addition, photodiodes 126, 127 are attached to proper portions of the SiOB 120 by considering an insertion position and an insertion angle of the WDM filters. SiOB 120 having the photodiodes 126 and 127 is attached to an SiOB 110, to which a laser diode 111 and a monitor photodiode 112 are attached. At this time, it is necessary to precisely align an end of the optical fiber 116 with the laser diode 111. Alternatively, the SiOB 120 having the photodiodes 126, 127 can be integrally formed with the SiOB 110 having the laser diode 111 and the monitor photodiode 112.
Operationally, with the module acting as a receiver, light incident into the optical fiber 116 is reflected from WDM filters 124, 125 and is introduced into the photodiodes 126, 127, so the photodiodes detect the light. At this time, the number of channels for incident signals may be increased by differently forming a wavelength of the incident light in each of channels.
When the module acts as a transmitter, a transmitting signal radiated from laser diode 111 is optically coupled with the optical fiber 130, and then, linearly proceeds to an exterior. To prevent transmitting and receiving signals from mutually interfering when simultaneously issued, it is necessary to form a wavelength of transmitting light differently from a wavelength of receiving light.
Problematically, however, for the conventional module structured with the SiOB having the photodiodes. It is impossible to assemble the module concurrently and integrally with the assembling process applied to a wafer. The need for a separate process entails extra expense, making it difficult to fabricate the optical module at a low price.
An added difficulty is that the receiving sensitivity of the photodiode may deteriorate depending on the insertion angle of a filter. Light reflected by a wavelength division multiplexing (WDM) filter propagates through free space and is incident into the photodiode. The propagation length of the light may depend on the insertion angle of the filter. If the insertion angle of the filter is 45°, the propagation length becomes minimized. If the radius of the optical fiber slightly exceeds 62.5, a minimum value of the radius of an incident beam at a surface of the photodiode is 62.5 sin(FFA of SMF) assuming a distance between an outer surface of the optical fiber and a surface of the photodiode is 0 (zero). At this time, the incident light, which has passed through an optical fiber core, continuously passes through a glass medium or a medium having a refractive index identical to the refractive index of the glass medium. Therefore, FFA of SMF may be about 4° taking into account the reflective index 1.5 of the medium when NA is 0.1 in a general free space. The radius of the incident beam at the surface of the photodiode is thus 17.
The optical transmitting/receiving module can be fabricated through a conventional technique as shown in FIG. 1 if an insertion angle of the filter is maintained at 45° since the diameter of incident light of a light receiving device of 1.25 GHz corresponding to a data speed of an E-PON bidirectional optical transmitting/receiving module of FTTH optical modules is ˜60. However, it is impossible, when the optical transmitting/receiving module is applied to a triplexer for FTTH, to maintain the insertion angle of the filter at 45°. For reference, a maximum incident angle of about 20° is realized through the current technique.